First of all, a conventional capacitance-type pressure sensor unit which is to be improved by the present invention will be described with reference to FIG. 14.
The capacitance-type pressure sensor unit shown in FIG. 14 includes a first insulating substrate 1 having a front surface formed thereon with an electrode (not shown) and a rear surface acting as a pressure sensing surface 1a and a second insulating substrate 2 combined with the first insulating substrate 1 to constitute a pressure sensor element 3. The second insulating substrate 2 has a rear surface provided thereon with an electrode (not shown) in a manner to be opposite to the electrode on the first insulating substrate 1 while being spaced therefrom at a predetermined interval and a front surface 2a provided thereon with a first circuit pattern (not shown). The first circuit pattern is electrically connected to the two above-described electrodes arranged in the pressure sensor element 3. The second insulating substrate 2 is mounted thereon with at least one electric circuit component 4 by soldering. The electric circuit component 4 is constituted by an integrated circuit or the like and electrically connected to the first circuit pattern to carry out processing of an output of the pressure sensor element 3.
The capacitance-type pressure sensor unit also includes a connector 5 arranged on a side of the front surface 2a of the second insulating substrate 2. The connector 5 includes a connector body or connector housing 6, which includes a base 6b having an end surface 6a kept contacted with the front surface 2a of the second insulating substrate 2 of the pressure sensor element 3 and provided therein with a circuit component receiving chamber 7 in which the electric circuit component 4 is received. Also, the connector 5 includes a plurality of connection conductors or connector terminals 8 which are supported in the connector body 6 and of which one end is arranged in the circuit component receiving chamber 7 and the other end is externally exposed.
The circuit component receiving chamber 7 of the connector 5 has a circuit board 9 arranged therein in a manner to be spaced at an interval from the front surface 2a of the second insulating substrate 2. The circuit board 9 is arranged in a manner to be interposedly supported between an annular support 10 made of an electrically insulating material and arranged on an outer peripheral edge of the front surface of the second insulating substrate 2a and a step 6c formed on an inner periphery of the base 6b of the connector body 6. The circuit board 9 is provided thereon with a second circuit pattern (not shown), which is electrically connected to the first circuit pattern on the front surface 2a of the second insulating substrate 2 and the connection conductors 8 of the connector 5. Connection between the connection conductors 8 and the second circuit pattern on the circuit board 9 is carried out by inserting one end 8a of each of the connection conductors 8 via each of through-holes formed via the circuit board 9 and soldering the end to a soldering electrode arranged on a rear surface of the circuit board 9. The circuit board 9 and the first circuit pattern on the front surface 2a of the second insulating substrate 2 are electrically connected to each other through electrical connection means 11 such as a flexible printed board or the like. The circuit board 9 thus connected is mounted thereon with electric circuit components 12a and 12b such as capacitors or the like for removing noise intruding thereinto through the other end 8b of each of the connection conductors 8 of the connector 5 by soldering.
The pressure sensor element 3, the circuit board 9, the base 6b of the connector body 6 and the like are received in a receiving casing 13 made of metal. The receiving casing 13 includes a bottom wall section 13a formed with a fluid inlet port 14 through which pressure measured fluid such as gas, liquid or the like of which a pressure is to be measured is introduced into the capacitance-type pressure sensor unit of the illustrated embodiment. The receiving casing 13 also includes a peripheral wall section 13b connected at one end thereof to the bottom wall section 13a, a cylindrical section 13c mounted on a central portion of the bottom wall section 13a so as to surround the fluid inlet port 14 and a threaded section 13d formed on an outer periphery of a distal end of the cylindrical section 13c. The pressure sensor element 3 is received in the peripheral wall section 13b of the receiving casing 13 in such a manner that the pressure sensing surface 1a is arranged opposite to the bottom wall section 13a and so as not to define a large gap between the pressure sensing surface 1a and the peripheral wall section 13b. The pressure sensing surface 1a of the pressure sensor element 3 and the bottom wall section 13a are arranged so as to define a fluid chamber 15 therebetween into which the pressure measured fluid is introduced. The peripheral wall section 13b has a seal member 16 arranged on a portion of an inner periphery thereof positioned between the pressure sensing surface 1a and the bottom wall section 13a. The seal member 16 is constituted by an O-ring for sealing the fluid chamber 15. Also, a seal member 17 is interposedly arranged between the base 6b of the connector body 6 and the peripheral section 13b of the receiving casing 13. The seal member 17 is constituted by an O-ring supported in a groove formed on an outer periphery of the base 6b. The connector 5 is fixed on the receiving casing 13 by holding the base 6a of the connector body 6 in an upper end section 13e of the receiving casing 13 by caulking.
In the conventional capacitance-type pressure sensor unit thus constructed, when pressure measured fluid such as gas, liquid or the like is introduced through the fluid inlet port 14 into the fluid chamber 15, a pressure of the fluid acts on the pressure sensing surface 1a of the first insulating substrate 1 of the pressure sensor element 3. Action of the pressure on the surface 1a permits a variation in capacitance between the electrodes arranged opposite to each other in the pressure sensor element 3. Such a variation in capacitance is converted into a voltage signal by a signal processing circuit constituted of the electronic circuit component 4 or the like. The voltage signal thus obtained is then outwardly transmitted through the connector 5.